1. Field of the Invention
The present invention relates, most generally, to an earth boring drill bit that includes cutting elements, and a method for forming the drill bit.
2. Background of the Invention
Various types of drill bits that include cutting elements are used in today=s earth drilling industries. The drill bits typically include cutting elements joined to pockets formed in the drill bit body, by brazing. In many bits, the pockets are formed in blade regions of the bit body. Drill bit bodies are commonly formed of a matrix material such as tungsten carbide. Drill bits are advantageously formed to include the matrix material in combination with a superabrasive material such as diamond crystals, also known as diamond grit. In such case, the matrix material is said to be impregnated with superabrasive material. The drill bit body may be formed to include the superabrasive impregnated matrix material in the blade or other regions of the bit body, or throughout the entire bit body.
GHIs (grit hot-pressed inserts), or PCD (polycrystalline diamond) or PCBN (polycrystalline cubic boron nitride) cutting elements are commonly mounted on the bit body. More particularly, the cutting elements are joined to the pockets or other cavities that extend into the bit body.
A shortcoming of conventional superabrasive impregnated drill bits, and the methods for forming such bits, is that the region of the bit body, for example the blades, that includes the cavities to which the cutting elements are typically joined by brazing, is often formed of superabrasive impregnated matrix material which provides additional hardness and strength to the blades, thereby providing a rock cutting ability to the blades. The presence of superabrasive materials in the impregnated matrix material, however, lowers the braze strength between the cutting elements and the bit body, more particularly, between the cutting element and the cavity to which the cutting element is joined by brazing. If the braze strength is weak, the cutting elements are prone to becoming disengaged from the bit body during drilling, causing early failure of the bit. Therefore, a shortcoming of the conventional art is that, while a superabrasive impregnated region of matrix material provides superior strength and hardness, it reduces braze strength between the drill bit body and the cutting elements. The present invention addresses these shortcomings.